May. 06, 2011

After we made the Newton's Cradle at Easter, we talked about Newton's laws on the Conservation of Energy. Don't worry, it was not an overly technical conversation for a six year old -- my memory and refresher course on classical mechanics only got me so far. But these basic laws govern sports like croquet, billiards and pool, curling, bowling, shuffleboard, and even marbles. They are easy enough to grasp, especially if you can play the sport or some version of it.

We started our research by visiting St. John's College here in Annapolis. It is my Alma Mater (Happy Mother's Day, I guess!) and the site of a grueling sports feud that is almost three decades old, the SJC vs. United States Naval Academy Croquet match. You can check out photos of the event in the slideshow below.

The legend states that a Johnny and a Middy met in Annapolis and the Middy boasted that he could beat the Johnny in any sport he chose. Well, the Johnny chose croquet, and the rest, as they say, is history. The Johnnies often win handily, though in recent years the Mids have put up some great teams and really given the Johnnies something to worry about.

My personal theory is that the Johnnies have a leg up because they study Newton and classical mechanics. Newton codified and explained the math that governs the movement of bodies alone and in contact with each other. The modern translation of Newton's First and Second laws are as follows:

First Law: Every body persists in its state of being at rest or of moving uniformly straight forward, except insofar as it is compelled to change its state by force impressed.

Second Law: The change of momentum of a body is proportional to the impulse impressed on the body, and happens along the straight line on which that impulse is impressed.

Robbie transferring energy from mallet to ball to ball

Beckett took his friend Robbie to a local park and we whacked the balls around, applying force in various ways. Hitting the ball straight on sent it on a straight path, but glancing it obliquely with the mallet sent it sideways. Similarly, if one ball struck another straight on, the second ball moved in the same direction as the first ball came from. If hit slightly off-center, the ball went sideways. There are an infinite number of variables and ways to do this, and everything affects the way the balls move: how thick the grass is, how level the pitch is, how much wind is blowing, and whether or not the mallet has any blemishes or imperfections on the head.

Ways to experiment:

What is the difference between transferring energy to a ball by hitting it directly with a mallet versus transferring energy to a ball by hitting one ball into another?

Does speed affect the friction that the grass provides? Is there anything that can be done to overcome the friction of the grass?

What would happen if you played croquet on a very hard surface, such as a parking lot?

You can see more of Newton's Laws at work with the other sports named above. A pool table, for example, is very smooth and offers very little friction to the balls. What if the felt was thicker -- how would that affect the game?

Curling is played with very heavy stones on ice. Why so heavy? What would happen if you played with much smaller stones, or even hockey pucks? Would it be easier or harder?

Bowling uses a very heavy ball and very heavy pins. Would the game change to have lighter balls or pins? Does a heavy ball make it easier to be accurate or harder?